8.16.3. Indstillinger

If the RGB radio button is clicked, a grey level image is
created with three layers (Red, Green and Blue), and two
channels (Grey and Alpha).

This function is interesting when using Threshold tool. You
can also perform operations like cutting, pasting or moving
selections in a single RBG channel. You can use an
extracted grayscale as a selection or mask by saving it in
a channel (right-click>Select>Save to a channel).

RGBA

If the RGBA radio button is clicked, a image is created
similar at the RGB Decomposing with a additional Alpha
layer filled with the transparencies values of the source
image. Full transparent pixels are black and the full
opaque pixels are white.

HSV

This option decomposes image into three greyscaled layers,
one for Hue, one for Saturation and another for Value.

Although Hue is greyscaled, it does
represent hues. In color circle, white and black are
starting and arrival points and are superimposed. They
represent Red color at top of circle. Grey intermediate
levels are corresponding to intermediate hues on circle:
dark grey to orange, mid grey to green and light grey to
magenta.

This option is similar to HSV. Instead
of the Value, the third layer contains
the image's L component.

CMY

This option decomposes image into three greyscaled layers,
one for Yellow, one for Magenta and another for Cyan.

This option might be useful to transfer image into printing
softwares with CMY capabilities.

CMYK

This option is similar at the CMY Decomposing
with an additional layer for Black.

This option might be useful to transfer image into printing
softwares with CMYK capabilities.

Alfa

This option extracts the image transparency stored in the
Alpha channel in
Channel dialog
in a separate image. The full transparent pixels are Black
the full opaque pixels are white. The graytones are smooth
transitions of the transparency in the source image.

LAB

This option decomposes image into three greyscaled layers,
layer “L” for Luminance, layer
“A” for colors between green and red, layer
“B” for colors between blue and yellow.

The LAB Decomposing is a color model of the Luminance-Color
family. A channel is used for the Luminosity while two other
channels are used for the Colors.
The LAB color model is used by Photoshop.

YCbCr

In GIMP there is four YCbCr
decompositions with different values.
Each option decomposes image in three greyscaled layers, a
layer for Luminance and two other for blueness and redness.

The YCbCr color model also called YUV is now used for
digital video (initially for PAL analog video). It's based
on the idea that the human eye is most sensitive to
luminosity, next to colors. The YCbCr Decomposing use a
transformation matrix and the different options are
different values recommended by ITU (International
Telecommunication Union) applied to the matrix .

Decompose to Layers

If this option is checked, a new grey-scaled image is created,
with each layer representing one of the channels of the selected
mode. If this option is not checked, every channel is represented
with a specific image automatically and clearly named in the name
bar.

Foreground as registration color

Eksempel 16.1. Crop marks

Source image

Cyan component

Black component

(Magenta and Yellow components omitted.)

This option is for specialists. It is related to CMYK printing.
When checked, every pixel of the current foreground color will
be black in each component of the decomposed images/layers. This
allows you to make crop marks visible on all channels, providing
a useful reference for alignment. A thin cross printed in
registration black can also be used to check whether the printing
plates are lined up.